# Understanding stress analysis of truss bridges

• Engineering
• Smushiehippo
In summary, the individual is seeking to understand the concept of truss bridges and where the maximum stress would be located in a single span truss bridge if it was evenly loaded. They also ask for clarification on whether their assumption that the maximum stress would be at the ends of the bridge is correct. The individual also mentions a homework problem related to analyzing the stress of a truss bridge and asks for help understanding where the first point of failure is likely to occur and if the results obtained from the analysis will accurately reflect real-life scenarios. They provide diagrams and equations for reference and ask for assistance in comparing the accuracy of the results based on the diagrams provided.

#### Smushiehippo

Homework Statement
analysis stress of truss bridge.
Relevant Equations
none
Hi

im trying to understand truss bridges.
Where would max stress be in single span truss bridge if it was evenly loaded across the bridge?

I thought single span truss bridge, max stress would be in the ends of the bridge. it would act like a simple supported beam with max bending motion being in centre. the truss would be located in the to chords of the beams.

Smushiehippo said:
Homework Statement:: analysis stress of truss bridge.
Relevant Equations:: none

Hi

im trying to understand truss bridges.
Where would max stress be in single span truss bridge if it was evenly loaded across the bridge?
A diagram indicating what you are trying to ask would be helpful. A truss is a group of structural members which can have any number of configurations.
Smushiehippo said:
I thought single span truss bridge, max stress would be in the ends of the bridge.
In a simply supported beam (with constant section modulus) the max normal stress occurs where the maximum bending moment occurs.

Smushiehippo said:
Homework Statement:: analysis stress of truss bridge.
Relevant Equations:: none

im trying to understand truss bridges.
Where would max stress be in single span truss bridge if it was evenly loaded across the bridge?
Is this question in relation to your other thread about FEA stress calculations? It would be nice if you replied in that other thread instead of creating new ones...

Smushiehippo said:
Homework Statement:: Explain where the first point of failure is likely to originate, and why.

An analysis of the studies, do you think that they will be an accurate representation of what will happen in practice?
Relevant Equations:: none

Hi

Im slightly stuck not sure what i put is ok.

FEA was used to carry out analysis on 3 structures and diagram results obtain (no data)
Explain where the first point of failure is likely to originate, and why.
An analysis of the studies, do you think that they will be an accurate representation of what will happen in practice?

Red indicates high stress and blue indicates low stress

For the (i) there is high stress at both ends and low stress in center. I believe 1st point of failure would be at centre (blue area) and not indicated on diagram of high stress (red). Trusses support the bridge and take the majority of the load and stresses. Blue section centre of the bridge and where load and stress will be most concentrated. contentrated stresses and loading will likely fatigue in beam.

For the (ii) there is high stress at each blade and low stress at the base. I believe 1st point of failure would be at blade (red). Impeller blade are the thinest point on the structure. strength in this area is lowest compared to base. excess high vibration could lead to fatigue and first point of failure.

For the (iii) there is high close to the small end and low stress in big end. I believe 1st point of failure would be at small end (red). connecting rod under goes compression and tension in operation. high speed causing high rpm lead to stretching of the rod leading to failure.

Im stuck on comparing accurcy. I believe (i) is inaccurate but (ii and iii) are accurate. how do i compare accuracy with only pics and no data. im not 100% what each pic is showing, eg compression, tension, deformation.

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erobz said:
A diagram indicating what you are trying to ask would be helpful. A truss is a group of structural members which can have any number of configurations.

In a simply supported beam (with constant section modulus) the max normal stress occurs where the maximum bending moment occurs.